1. Field of the Invention
This invention relates generally to orientation sensors, and more particularly to an improved sensor for producing electrical signals corresponding to angular position about a generally horizontal axis.
2. Brief Description of the Prior Art
It is well established that a spirit (or carpenter's) level comprised of a transparent elongated vial enclosing a fluid and a bubble can be used to indicate a level orientation. Further, it has been recognized that the light transmission, reflection or refraction characteristics associated with a fluid-filled spirit level can be utilized by light sensitive electronic devices to remotely and more accurately sense level status. For example, U.S. Pat. No. 4,154,000 shows a transparent elongated spirit level device utilizing pairs of concentrated light beam sources and photodetectors configured so that the position of a bubble can be sensed by the disruption of a refracted light beam's path through a liquid. Such a device, using two pairs of sources and detectors located near the middle of the vial, can fairly effectively determine whether a "level" condition exists. However, if measurement of the off-level angle is desired, additional source/sensor pairs spaced along the length of the vial must be employed. In such a configuration, the position of the bubble in the vial (which corresponds to the off-level angle) is determined by which of the source/detector beams has been interrupted. However, the precision of such a device's measurements is severely limited by the number of source/detector pairs employed, which is usually limited by space constraints and beam overlap considerations. Further, the angular range of measurement of such an elongated spirit level is usually limited to just a few degrees off-level.
International Pat. App. No. PCT/F189/00083 discloses an elongated spirit level device in which multiple sources are mounted along the side perimeter of the vial, and a photodetector is mounted directly below the center of the vial. As the light sources are sequentially lit, readings are taken from the photodetector measuring the amount of light reflected from the bottom of the bubble. After readings have been taken corresponding to all of the sources, a computer can compare the readings and determine the bubble's location within the vial. It is evident that such an arrangement would require complex electronics to perform the sequential lighting of the sources and the corresponding synchronous measurements of the photodetector Further, the speed of such a device is necessarily limited by the speed at which the sources can be sequentially turned on and off, as well as the speed at which the computer can measure, process and compare the photodetector readings.